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6 sp manual downshifting effect mpg?

Discussion in 'Technical Chat' started by MMazz365, Apr 8, 2011.

  1. Apr 8, 2011 at 8:18 AM
    #1
    MMazz365

    MMazz365 [OP] Well-Known Member

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    I have a 2010 trd off road 6 speed manual and I downshift to every stop and slow down. Recently I've been trying to get rid of my lead foot but I still see I'm blowing through gas like no other... down downshifting effect this?
     
  2. Apr 8, 2011 at 8:26 AM
    #2
    hudhawk

    hudhawk #texasforever

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    Considering downshifting will raise rpms, and at higher rpms the engine burns more fuel, i would think so. I also drive a trd offroad w/ 6spd manual, given it is an 05, not an 11, but i would think it would be the same. I stopped downshifting to slow down when im driving around town and started taking it out of gear and using the brake to slow down. My mpgs went up a little. What are you currently getting in terms of mpgs?
     
  3. Apr 8, 2011 at 8:34 AM
    #3
    MMazz365

    MMazz365 [OP] Well-Known Member

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    Honesty idk but it has to be low bec I need to fill up every 3 days at least. I wanna invest in ( I forget the name) that computer that will tell you
     
  4. Apr 8, 2011 at 8:40 AM
    #4
    hudhawk

    hudhawk #texasforever

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    Its called a scanguage. Every 3 days is pretty bad, lol. I can usually make it a week on one tank, that is unless my 18 year old go fast mechanism kicks in, haha.
     
  5. Apr 8, 2011 at 8:50 AM
    #5
    MMazz365

    MMazz365 [OP] Well-Known Member

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    Lol that's what its called... and haha that's what I'm trying to eliminate, my 18 yr old fast mechanism lol
     
  6. Apr 8, 2011 at 8:50 AM
    #6
    MMazz365

    MMazz365 [OP] Well-Known Member

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    Did you mean I save gas by downshifting?
     
  7. Apr 8, 2011 at 8:54 AM
    #7
    thinkingman

    thinkingman Well-Known Member

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    Foglights are for fog, not oncoming traffic!
    Downshifting neither helps you slow down or save fuel.
    Add another to the TW misinformation machine.
    The only benefit is to the mechanic that will be replacing your clutch at a much-too-early interval.
    You guys kill me.
     
  8. Apr 8, 2011 at 8:57 AM
    #8
    steve o 77

    steve o 77 braaap

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    It does help you slow down. Have you ever had the truck in 4low going down a steep incline just coasting in 1st gear? you don't even have to use the brakes because the compression of the engine keeps the speed constant.

    Now I agree downshifting to slow down at every light is kinda stupid unless you're able to perfectly rev match the engine on every shift because you will kill the clutch sooner.
     
  9. Apr 8, 2011 at 8:58 AM
    #9
    jrider636

    jrider636 Well-Known Member

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    so true and lmao
     
  10. Apr 8, 2011 at 9:00 AM
    #10
    skytower

    skytower Well-Known Member

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    Hmmm... I have to call BS. Downshifting, also known as Engine Braking, has a significant effect on deceleration. Fuel savings, however, is still debatable.
     
  11. Apr 8, 2011 at 9:02 AM
    #11
    MMazz365

    MMazz365 [OP] Well-Known Member

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    For a fact, downshifting helps me slow down significantly
     
  12. Apr 8, 2011 at 9:10 AM
    #12
    macgyver

    macgyver Well-Known Member

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    Actually, Complete misinformation on your part sir

    Downshift DOES slow you down and DOES NOT wear your clutch any faster if done properly.

    I downshift all them time and always have in every manual vehicle I have driven.

    Explain to me why when rolling down a hill in 1st gear as opposed to nuetral I go slower?
    Why do I spin out of control on an icy hill coasting in nuetral using my brakes but I don't when I'm slowly crawling down the hill in 1st gear without using my brakes?
    Ever descended a hill in 4LO in first gear? When I offroad I rarely have to use my brakes descending hills because I can crawl down in 1st gear without touching my brakes.
    Why are there signs on the side of road in mountains telling truckers to use a lower gear?

    to the OP, when decellerating you actually use less fuel than if you were coasting in nuetral, then transfer of power through the driveline keeps the engine turning as opposed to in nuetral your engine would require fuel to keep it idling.

    For example, in my last car I had a wideband 02 readout on my dash because I wanted to monitor my AFR's since I was turbo'ed. When I would downshift, my wideband readout would show "LEAN" when decellerating in gear. If I coasted and used my brakes, my wideband readout would display around 14.7 (stoich). This means I was using LESS fuel downshifting than if I coasted in nuetral. RPM's aren't the only indicator of fuel consumption.

    One might actually use more fuel doing 20mph in 5th gear @1500rpm as opposed to running 20mph in 3rd @ 3000rpm because the engine is under more load at 20mph in 5th gear which requires more fuel to keep it from stalling.
     
  13. Apr 8, 2011 at 9:17 AM
    #13
    Foihdzas

    Foihdzas VA7PTZ

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    I always downshift when coming up to a light, going down steep grades ect... although it does not give me a huge deceleration, it does help. I do agree with thinkingman about premature clutch wear, so do not downshift aggressively, ( 5th to 3rd, then 3rd to 1st kind of thing) so I do not wear my clutch out too badly.

    my 0.02
     
  14. Apr 8, 2011 at 9:24 AM
    #14
    hudhawk

    hudhawk #texasforever

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    I'd much rather buy new brake pads than a new clutch
     
  15. Apr 8, 2011 at 10:03 AM
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    thinkingman

    thinkingman Well-Known Member

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    Foglights are for fog, not oncoming traffic!
    If you read the posits in the OP, and you have experience in the matter, you'll find that downshifting to a stop and maintaining speeds on downgrades are two entirely different matters.
    In re downshifting, I'd be willing to bet less than 10% of the people on this thread know how to heel and toe properly and if you're trying it in a Tacoma, it's a raging fail, with the brake/clutch/accelerator and sloppy-ass shifter.
    I learned to heel and toe in a Formula Ford and promise you, it wasn't for slowing the car.
    Creeping downhill in 4wd is not the same as the OP.
    No it's not.
    Trucks using lower gears to control forward momentum on downgrades is not the same as the OP...some may use an exhaust brake for additional control, but that's a different kettle of fish.

    Why do I spin out of control on an icy hill coasting in nuetral using my brakes but I don't when I'm slowly crawling down the hill in 1st gear without using my brakes?
    Because you're not a very good driver and lack basic car control knowledge.
    Low friction surfaces require very light inputs if you're nearing maximum traction. I know, without a doubt, I can modulate my brakes quicker and with more precision, than I can modulate the throttle, especially if I have to alternate between a closed throttle and an open one....in your example I italicised above, you're adding drivetrain backlash into the equation.....epic fail in low traction/downhill circumstances.
    Stick to the example by the OP, not your own.
     
  16. Apr 8, 2011 at 10:18 AM
    #16
    skunk

    skunk what did I miss?

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    The ECU control with the manuals makes the EPA MPG rating worse on the 6 spd than the autos.

    I have noticed that when coasting in neutral the speed sensors must tell the RPMs to stay elevated (~1200) until you come to a stop and then it goes to warm idle (~800).

    Because of this I usually leave it in gear while braking to keep the RPM's down and then I put in Neutral as I come to a halt.

    I just wish an EE would come up with some sort of Flash fix to take the ECU emission control out of the equation. It takes the fun out of a manual when the RPM's don't drop when you let off the gas.:(
     
  17. Apr 8, 2011 at 10:22 AM
    #17
    buck

    buck the-eh-team.com

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    Your statements make no sense.

    Downshifting does slow the vehicle due to engine braking, requiring less brake application to get the same amount of deceleration.

    Downshifting with no accelerator input cuts injector pulses above certain RPM's. Downshifting does have potential to save gas. When your engine is at idle speed while coasting to a stop, the injectors are pulsing thus using gas to maintain RPM's. Downshifting does put additional stresses on the drivetrain and clutch plate, but that can be minimized with reasonable rev-matching.

    Your talk about heel-toe has nothing to do with this thread. Heel-toe for your application on a track where grip is at it's limits is completely different in purpose for street driving and downshifting. How often are we downshifting while at the limits of traction on the street? You match-rev on a track to disrupt as little as possible the contact patch friction limits.
     
  18. Apr 8, 2011 at 10:23 AM
    #18
    Hondarider08

    Hondarider08 "That's what she said..."

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    While I'll let the others argue about something completely off topic... I'll add my two cents into the actual question. :rolleyes:

    I have a 4.0 liter 6spd and I was always curious about the effects of downshifting on MPG's. I broke down about a month ago and bought an ultra-gauge. This gauge has an instantaneous MPG window and also has a open loop closed loop indicator. When driving normally down the road it shows an closed loop. As I go to slow down at a stop light, I put it into neutral and watch the mpg's as I'm coasting. They take a large jump up, but then slowly drop down as my speed drops as well. Then at the next stop light I try it with a downshift. My loop indicator then shows an open loop (injectors are cut off). My mpg's go up quickly, but they dont seem to drop down quite as quickly.

    So to sum it up, downshifting does seem to help with milage. I dont think it's hugely significant, but enough to notice. As long as your not revving the shit out of your motor or going from an extremely high speed to a slow speed by downshifting, then you should see an increase. As far as clutches go, like I said, as long as you're not abusing it and be gentle, you shouldn't have any problems. I downshift everywhere and my clutch still feels the same as the day I got the truck.

    Thats my two cents.
     
  19. Apr 8, 2011 at 10:27 AM
    #19
    Evil Monkey

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    It does save gas according to my aeroforce gauge. The injectors don't shut off as some have claimed (Injector pulse width drops to about 2ms in a 20ms period meaning it's pumping gas about 10% of the duty cycle). It isn't much better than coasting though. So I doubt you'd save much over just coasting and braking.

    Engine braking does slow the vehicle down though. To test it, put the vehicle in neutral and coast. The put the vehicle in gear and let out the clutch. You'll observe the vehicle slowing much quicker.
     
  20. Apr 8, 2011 at 10:32 AM
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    Evil Monkey

    Evil Monkey There's an evil monkey in my truck

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    It's not burning more fuel. In fact the injectors are at their lowest fuel rate when you're off the accelerator. The reason the rpms are higher is because the drive train is mechanically linked to the engine. The engine has to turn at the same rate which is why the rpms jump.
     
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